This invention relates generally to ECP freight train braking systems and, more particularly, to a method for implementing low power ECP trainline communications whereby power consumption is reduced to a level such that sufficient power can be provided by a standard locomotive battery to indefinitely power the ECP equipment on each car.
The AAR has defined rail industry specifications for Electrically Controlled Pneumatic (ECP) braking based upon use of Echelon LonWorks, PLT-10A power line overlay transceiver version, as the means to communicate between cars and the lead locomotive. The communication specifications, as presently defined, require the Echelon transceiver to be "on" at all times, in order to be ready to receive brake commands from the locomotive, as well as to respond to routine status polling requests.
The Echelon transceiver has a power demand of approximately 300 mW when in receive mode and 2.5 W when transmitting. Message lengths for transmissions are typically on the order of 20 ms long. The average car transmission duty cycle is on the order of two times per minute (except for the last car in the train, which transmits each second). Therefore, the average power demand associated with the Echelon transceiver is on the order of 320 mW.
The AAR specifications allow an average power budget of 10 W per car. To supply this level of power, it is necessary to provide a nominal 230 VDC trainline, for a 160-car train, with a 12,000-foot length. This has resulted in the need for a 74 to 230 VDC DC-DC power supply on a locomotive in the consist, with a power rating of 2,500 W, to provide sufficient ECP power for 160 cars and losses due to cable resistance.
A low-power ECP system emulation system with an average power requirement budget under 500 mW in "emulation" mode is disclosed in commonly owned copending U.S. patent application Ser. No. 09/224,540, titled "RAILWAY EMULATION BRAKE," filed on Dec. 31, 1998, and is hereby incorporated herein by reference. That system provides for powering an "all electric" ECP valve system using the 74 VDC from the locomotive, while emulating a conventional pneumatic service valve operation. The power budget for that system is based upon use of the Echelon transceiver only for system set-up and alarm reporting. It does not allow for the full ECP functionality of electrically activated brake application and graduated release of brakes. The addition of approximately 320 mW associated with having the Echelon continuously on for full ECP functionality cannot be afforded in a power budget low enough to operate on 74 VDC.
Additionally, commonly owned copending U.S. patent application Ser. No. 09/224,541, titled "RAILWAY LOCOMOTIVE ECP TRAINLINE CONTROL," filed on Dec. 31, 1998, is also hereby incorporated herein by reference.
In a very low power ECP trainline type of system the Echelon receiver cannot be powered all the time, as it is in a conventional system, since the Echelon receiver consumes too much power. Thus it is necessary to provide for a "Master Controller" ("MC") on the locomotive, i.e. the HEU, to tell each freight car in the train to turn its Echelon receiver "on" so that the MC can issue commands to the freight cars. Also, in a low power ECP system, since the communications device, i.e. the Echelon transceiver, is normally turned off, it is necessary to provide for each car to periodically report their status to the MC. Moreover, failure conditions need to be handled in a safe manner.
Accordingly, there is a need for a low power ECP communication system wherein the Echelon transceiver is operated on an intermittent basis, as needed to reduce the average power demand under 100 mW, while still providing full functionality, per AAR ECP specifications. Thus, a fully functional ECP system can be provided with the power supplied by the standard 74 VDC locomotive battery along with the safe management of failure conditions.